The present invention relates generally to a recorder, and more particularly to a retainer for a recording medium in the recorder. The present invention is suitable, for example, for a clamping device that fixes a disc onto a spindle hub in a hard disc drive (“HDD”).
Along with the recent spread of the Internet etc., a demand for fast recording of a large amount of information is growing. A magnetic disc drive, such as an HDD, is required to have a larger capacity and an improved response. For the larger capacity, the HDD narrows a track pitch on the disc and increases the number of installed discs. For the improved response, use of a higher speed spindle motor is promoted.
Plural discs are stacked around a hub that is fixed around a rotating shaft of the spindle motor, and capped by a clamp ring. The clamp ring fixes these discs when the clamp ring is screwed onto the hub. The number of screws is one, three, four (Japanese Patent Application, Publication No. 2001-331995), six, etc. The clamp ring and the screw(s) rotate with the disc.
A recent high-density disc requires highly precise head positioning. It is thus necessary to restrain vibrations applied to and deformations of the disc, and to correct a weight imbalance (simply referred to as “imbalance” hereinafter) around the spindle motor axis. A primary factor of the imbalance is an imbalance between the disc and the spindle motor moving part. Various imbalance correcting methods are known, such as a first method that reduces an aperture between the disc and the spindle hub, a second method for moving a disc to a balancing position, and a third method that attaches a balancer.
As more precise head positioning is required, the influence due to the clamp ring, i.e., an offset between a center of gravity and a rotating center of the screwed clamp ring becomes non-negligible. The first method does not correct the clamp ring caused imbalance, and has a difficulty in reducing the imbalance. The second and third methods can correct the clamp ring caused imbalance, but they need to correct both the imbalance of the clamp ring and the imbalances of the disc and the spindle motor moving part. The second method results in a large moving amount of the recording medium. The third method requires a large weight.
Methods of reducing the clamp ring caused imbalance include a fourth method that restricts a clamping position by a close engagement between the spindle motor and the clamp ring, and a fifth method that uses a jig and restricts a clamping position in assembly. The HDD hates dust or particles caused by contact frictions, and requires an aperture in assembly. Therefore, the fourth method has a limited restricting amount. The improved working precision to the components is needed for a narrow aperture, but this would result in an increased cost. In addition, the fifth method disadvantageously requires a highly precise facility.
Thus, the clamp ring should be made slightly larger, and the imbalance amount should be eliminated by a simple method.